engleski

CHANGES DETECTED IN SEASONAL CLIMATOLOGIES OF THE NORTHERN ADRIATIC BASIN

Thermohaline and bio-chemical properties of over 13˙000 oceanographic stations collected in the northern Adriatic Sea during the period 1970-2007 have been analyzed. Data were extracted from MEDAR/MEDATLAS2002 and ISMAR-CNR database. All data have been divided in two periods in order to define the seasonal climatologies and to show variations in last two decades (1990-2007) respect to the reference period (1970-1989). Statistical analysis of annual and seasonal time series of atmospheric data at selected locations around the northern Adriatic basin and Po river runoff reveals in several cases significant trends which can be related to the observed changes in marine fields. In particular, relevant variations (both negative and positive, according to the season) are evident in the surface haline field, while very limited variations are detected at intermediate and bottom layers. Marine temperatures at surface show a strong warming in autumn, winter and spring, while the summer period does not exhibit relevant changes ; the behavior is more variable at deeper layers. Seasonal analysis of bio-chemical climatologies show relevant variations. A general chlorophyll-a reduction is particularly evident in winter season. Dissolved oxygen values in surface layer show seasonal changes mainly influenced by sea temperature, with the maximum values in winter period and the lowest values in summer period. In last two decades a general decrease of pH values has been recorded in entire sub basin, in all seasons, and in all layers, except for spring when higher values reported in area near Po River delta are probably caused by fluctuations of river inflow. Besides salinity of the northern basin, changes in Po River inflow and its seasonal peaks influence nutrient inputs. In the last two decades, a relevant increase of nutrient concentrations has been recorded in surface layer in winter period (except for nitrites), together with increase in spring and autumn (except for nitrites and phosphate), while a decrease of all nutrient salts has been reported in summer period. The latter anomalies directly derives from the reduced Po River runoff, while the winter anomalies are only partially justified by the increased Po River runoff and more complete explanation can be given by looking at chlorophyll, which confirm that less nutrients are utilized by photosynthesis. Anthropogenic effects acting in different directions, like intensive farming in Po valley and phosphate reduction introduced by Italian legislation, play a role in such changes.

Seasonal climatologies; Adriatic Sea

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